Executive SummaryThe External Flowsheet Review Team (EFRT) expressed concern about the potential for Waste Treatment and Immobilization Plant (WTP) pipe plugging. Per the review's executive summary, "Piping that transports slurries will plug unless it is properly designed to minimize this risk. This design approach has not been followed consistently, which will lead to frequent shutdowns due to line plugging." To evaluate the potential for plugging, critical-velocity tests were performed on several physical simulants to determine if the design approach is conservative. Critical velocity is defined as the point where particles begin to deposit to form a moving bed of particles on the bottom of a straight horizontal pipe during slurry transport operations. The critical velocity depends on the physical properties of the particles, fluid, and system geometry.This report gives the results from critical-velocity testing and provides an indication of slurry stability as a function of fluid rheological properties and transport conditions that are typical of what the plant will see. The experimental results are compared to the WTP design guide on slurry-transport velocity in an effort to confirm minimum waste-velocity and flushing-velocity requirements as established by calculations and critical-velocity correlations in the design guide. The major findings of this testing are as follows:Experimental results indicate that for Newtonian fluids, the design guide is conservative. The design guide is based on the Oroskar and Turian (1980) correlation, a traditional industry-derived equation that focuses on particles larger than 100 m in size. Slurry viscosity has a greater effect on particles with a larger surface area to mass ratio, i.e. smaller particles. The increased viscous forces on small particles result in a smaller critical velocities. Since the Hanford slurry particles generally have large surface area to mass ratios, the reliance on such equations in the 24590-WTP-GPG-M-0058, Rev 0 design guide (Hall 2006) is conservative. Additionally, the use of the 95% percentile particle size as an input to this equation is conservative. The design guide specifies the use of the d 95 density, this term is ambiguous and needs clarification in the design guide. Nonetheless, this value is interpreted to mean the density of the d 95 particle. This density value is irrelevant for critical velocity calculations. Often this value is unknown, and Equation 1 of the 24590-WTP-GPG-M-0058, Rev 0 design guide (Hall 2006) will be used for design purposes. This equation calculates an average or composite density of all solids in the slurry. However, test results indicate that the use of an average particle density as an input to the equation is not conservative. Particle density has a large influence on the overall critical-velocity result returned by the correlation. The viscosity correlation used in the WTP design guide has been shown to be inaccurate for Hanford waste feed materials. Additionally, the recommendation of a 30% minimum margi...

Most correlations/models for minimum transport or critical velocity of slurry were developed for slurries composed of particles greater than ∼100-200 m diameter with narrow particle-size distributions which is typical of the minerals industry. Many other process industries handle smaller particles. In particular waste slurries at the U.S. Department of Energy's Hanford Site have broad size distributions and significant fractions of smaller particles. Despite the size of these wastes, recent studies at Pacific Northwest National Laboratory indicate that the small particles might be of sufficient density to pose a significant risk for pipeline deposition and plugging. To allow predictive assessment of deposition of fine dense particles for waste slurry transport at the U.S. DOE Hanford site, a pipeline-transport correlation for critical velocity was developed using a simple power-law between two dimensionless numbers important for slurry transport, the deposition Froude and Archimedes numbers. The correlation accords well with experimental data for slurries with Archimedes numbers <80 and is an adequate pipeline design guide for processing Hanford waste slurry.La plupart des corrélations/modèles pour le transport minimum ou la vitesse critique des boues liquides ontété développés pour des boues liquides composées de particules de diamètre supérieurà ∼100-200 m avec des distributionsétroites des tailles des particules qui sont typiques de l'industrie minière. De nombreuses autres industries de transformation gèrent les particules plus petites. En particulier, les boues liquides des déchets du site de Hanford du Département américain de l'Énergie (DOE) présentent de larges distributions de taille et des fractions significatives de particules plus petites. En dépit de la taille de ces déchets, desétudes récentes du Pacific Northwest National Laboratory indiquent que les petites particules pourraientêtre de densité suffisante pour poser un risque significatif de blocage et de dépôt des canalisations. Pour permettre uneévaluation prédictive des dépôts de petites particules denses pour le transport des boues liquides des déchets au site de Hanford du DOE américain, une corrélation pipeline-transport pour la vitesse critique aété développée en utilisant une simple relation exponentielle entre deux nombres adimensionnels importants le transport des boues liquides, le dépôt Froude et les nombres d'Archimède. La corrélation correspond bien avec les données expérimentales pour les boues liquides présentant des nombres d'Archimède <80 et constitue un guide de conception adéquat des canalisations pour le traitement des boues liquides des déchets de Hanford.

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